Preparation of 2,5-dimethylhexadienes

ABSTRACT

Selective formation of 2,5-dimethylhexadiene-2,4, or mixtures of the same with the corresponding 2,5-dimethylhexadiene-1,4, or of the latter with 2,5-dimethylhexadiene-1,5 in good yield is achieved by the vapor phase ring opening dehydration of 2,2,5,5tetramethyltetrahydrofuran, using alkali or platinum selected metal oxide catalysts at varying temperatures and liquid hourly space velocities.

Unite States Thopson atent 51 Sept. 19,1972

[54] PREPARATION OF 2,5-

DHMETHYLHEXADIENES [72] Inventor: Robert M. Thompson, Wilmington,

Del.

[52] US. Cl. ..260/681 R [51] Int. Cl ..C07c 11/12 [5 8] Field of Search..260/681 [56] References Cited UNITED STATES PATENTS 2,737,535 3/1956Taylor et a1. ..260/668 2,910,520 10/1959 Guest et al ..260/68l FOREIGNPATENTS OR APPLICATIONS 506,038 5/1939 Great Britain ..260/68l OTHERPUBLICATIONS Catalytic Transformations of Heterocyclic Com pounds Yuryeret al. Journal of General Chemistry U.S.S.R. 1956 pp. 293- 296, Vol. 26.

Primary Examiner-Delbert E. Gantz Assistant Examiner-J. NelsonAttorney-George L. Church, Donald R. Johnson, Wilmer E. McCorquodale,Jr. and Stanford M. Back [57] ABSTRACT Selective formation of2,5-dimethylhexadiene-2,4, or mixtures of the same with thecorresponding 2,5- dimethylhexadiene-1,4, or of the latter with 2,5-dimethylhexadiene-l,5 in good yield is achieved by the vapor phase ringopening dehydration of 2,2,5,5- tetramethyltetrahydrofuran, using alkalior platinum selected metal oxide catalysts at varying temperatures andliquid hourly space velocities.

8 Claims, NoDrawings PREPARATION OF 2,5-DIMETHYLI-IEXADIENES BACKGROUNDOF THE INVENTION This invention relates to the formation of 2,5-dimethylhexadiene isomers. More particularly, this invention relates tothe ring opening dehydration of 2,2,5,5-tetramethyltetrahydrofuran(TMTHF) with certain metal oxide catalysts to form selectively either2,5-dimethylhexadiene-2,4 (-2,4); or mixtures of 2,4, with2,5-dimethylhexadiene-l,4 (-l,4); or mixtures of -l,4 with2,5-dimethylhexadiene-l,5 (-l,5), all of which are useful ascross-linking agents and as monomers for copolymers in the area ofplastics and elastomers.

J. Gen. Chem., U.S.S.R., 26, 293-6 (I956) teaches that treatment of2,2,5,5-tetramethyltetrahydrofuran with alumina in the presence of steamyields 50 percent of -2,4, and 18 percent of l ,5, while catalyticdehydration of the corresponding diol yields 60 percent of -2,4, and 9percent of l ,5. Thus, selective formation of the 2,4, or formation ofthe corresponding -l,4 isomer is neither taught nor suggested by thisprior art reference.

SUMMARY OF THE INVENTION It has now been found, in accordance with thepresent invention, that by the judicious selection of certain metaloxide ring opening dehydration catalysts, it is possible to convert2,2,5,5-tetramethyltetrahydrofuran to selected 2,5-dimethylhexadieneisomers wherein at most two of the three possible isomers are formed tothe substantial exclusion of the third, and often just one of saidisomers is formed, thereby facilitating separation and recovery of saidisomers.

Thus, in one embodiment of this invention, it has been found that whenTMTHF is contacted with a platinum-on-alumina reforming-type catalyst,or with a base-washed alumino-silicate zeolite catalyst, within certainspecified temperature ranges, there is obtained the -2,4 isomer to thesubstantial exclusion of any of the other isomers. In addition to goodselectivity for the -2,4 isomer, yields of from 40 to 80 percent byweight are readily obtainable.

In this and each further embodiment of the invention, the catalytic ringopening dehydration is conveniently achieved by admixing the TMTHF witha carrier gas such as hydrogen or nitrogen, passing the mixture in avapor phase over a bed of selected catalyst at varying liquid hourlyspace velocities (LHSV) and temperatures, and recovering and separatingthe various isomers. The TMTI-IF is desirably admixed with the carriergas in mole ratios of 4 to l, with an LHSV of about 0.5 to 1.5, andpreferably about I.

In the case of the platinum-on-alumina catalyst, it is preferred thatthe reaction be carried out at a temperature of from about 360 to 470 C,and preferably 440 to 460 C, at an LHSV of about 0.7 to 'l.3, andpreferably l.0. When these reaction conditions are employed, the productis comprised substantially of the 2,4 diene. However, surprisingly, ithas further been found that when both the temperature and flow rate aresubstantially reduced, i.e., when the temperature is in the range ofabout 350 to 370 C, and the LHSV is about 0.8 to 1.2, there is producedinstead a major proportion of the -l ,4 diene with only a minorproportion of the -2,4 diene. Thus, by using the same catalyst butvarying the reaction conditions the nature of the final product may becarefully controlled. The catalyst used in this embodiment of theprocess is any commercially available alumina catalyst havingimpregnated therein from about 0.l to 1.0 percent by weight of platinum,and preferably about 0.5 percent of platinum, as for example RD-l 50(Englehard Industries, N.J., USA).

The 2,4-diene, as aforestated, may likewise be formed to the substantialexclusion of the other isomers when a base-washed alumino-silicatezeolite catalyst is employed at temperatures of about 200 to 270, andpreferably 245 to 265 C, at an LI-ISV of about 0.5 to 1.3, andpreferably 1.0. The catalyst is desirably any commercialalumino-silicate zeolite which is 10 to percent crystalline by X-ray,and contains an exchanged alkali metal using 10 to 100 percent ofexchange capacity (for example sodium-washed Linde type Y zeolite).

In a further embodiment of this invention, it has been found thatmixtures of two of the three isomers may selectively be formed whendifferent metal oxide catalysts are substituted for those describedabove, For example, when an activated alumina is employed, attemperatures of about 250 to 400 C, and preferably 250 to 300 C, and anLHSV of about 0.8 to 1.2, and preferably 1.0, mixtures of the -2,4 dieneand -l ,4 diene are obtained, wherein the -2,4 diene is the predominantspecies. These two isomers are readily separated by distillation. Thecatalyst may be any commercially available activated alumina, such asF-l0 (Alcoa Corp., U.S.A.).

In still a further embodiment of this invention, it has been found thatwhen there is employed a base-washed sintered metal oxide such as analuminum silicate-aluminum oxide mixture, e.g., Corhart (CorhartRefractories Co., U.S.A.), at temperatures in the range of from 475 to525 C, and preferably 480 to 510 C, at an LHSV of from 0.8 to 1.5, andpreferably 1.0, there is obtained a mixture of the -l ,4 and -1,5dienes. Corhart,

particularly when it has been neutralized, is generally an inertmaterial, at least for purposes of this invention, when contacted withreactants at temperatures below about 400 to 450 C.

The various embodiments of this process will now be illustrated by thefollowing examples.

EXAMPLES l-9 A series of runs was carried out using a flow reactor fedby a constant-speed syringe pump containing a mixture of carrier gas andTMTHF in amounts of 4 moles of gas to 1 mole of TMTl-IF. The flowreactor was provided with an inert material (base-washed Corhart) in aheating zone which served to vaporize the TMTHF, fol lowed by a catalystbed. The pump was adjusted to provide varying flow rates at differenttemperatures, depending upon the catalyst employed. Except whereindicated, the LHSV was I, i.e., 20 cc/hr. of TMTHF/2O cc of catalyst.

The resulting vapors were then trapped within ice water traps andanalyzed by vapor phase chromatography to give the results shown inTable I below.

TABLE I Car- Corner Temp rier Gas C Gas Flow Products tn) l RD-l50 360H, 30 l 20 5 60 2 RD-l50" 455 H 120 l 80 3 F-l Alumina 350 N, 60 l 60 2l8 4 FlO Alumina 300 N 60 l 82 l2 5 F-lO Alumina" 250 I1 60 l 88 l2 6Base-Washed Corhan 500 N 60 3/2 I 25 24 7 Base-Washed Corhan 400 N 60 l8 NaY Zeolite 200 N2 60 l 40 9 NaY Zeolite 250 N 60 l 65 l0 NaY Zeolite270 N 60 l 42 ""cc/mn ""weight percent alumina with 0.5 weight percentplatinum "activated alumina "sodium-washed Corhart sodium-exchangedLinde type Y zeolite What is claimed is:

1. A process for the preparation of 2,5-dimethylhexadiene-2,4 whichcomprises contacting tetramethyltetrahydrofuran in a vapor phase with acatalyst selected from the group consisting of platinum-on-alumina andan alkali metal exchanged crystalline alumino-silicate zeolite at anelevated temperature, wherein said temperature is at least 360 C whenthe platinum-on-alumina catalyst is employed.

2. The process according to claim 1 wherein thetetramethyltetrahydrofuran in contacted with the platinum-on-aluminacatalyst at a temperature in the range of from about 360 to 470 C at aliquid hourly space velocity of about 0.7 to 1.3.

3. The process according to claim 1 wherein thetetramethyltetrahydrofuran is contacted wjth the alkali metal exchangedalumino-silicate zeolite at a temperature in the range of from about 200to; 350 C at a liquid hourly space velocity of about 0.5 to l 4. Aprocess for the preparation of a mixture of 2,5- dimethylhexadiene-2,4and 2,5-dimethylhexadienel ,4 which comprises contacting tetrahydrofuranin a vapor phase with a catalyst selected from the group consisting ofplatinum-on-alumina and activated alumina at an elevated temperature,wherein said temperature is no greater than 360 C when the platinumon-alumina catalyst is employed.

5. The process according to claim 4 wherein thetetramethyltetrahydrofuran is contacted with the platinum-on-aluminacatalyst at a temperature in the range of from about 350 to 370 C at aliquid hourly space velocity of about 0.7 to 1.3.

6. The process according to claim 4 wherein thetetramethyltetrahydrofuran is contacted with the activated aluminacatalyst at a temperature of from about 200 to 270 C, at a liquid hourlyspace velocity of about 0.5 to 1.3.

7. A process for the preparation of a mixture of 2,5-dimethylhexadiene-l,5 and 2,5-dimethylhexadiene- 1,4, which comprisescontacting tetramethyltetrahydrofuran in a vapor phase with a catalystcomprising an alkali metal exchanged aluminum silicate aluminum oxidemixture oxide at an elevated temperature.

8. The process according to claim 7 wherein the reaction is carried outat a temperature in the range of from about 475 to 525 C, at a liquidhourly space velocity of about 0.8 to 1.2.

2. The process according to claim 1 wherein thetetramethyltetrahydrofuran in contacted with the platinum-on-aluminacatalyst at a temperature in the range of from about 360* to 470* C at aliquid hourly space velocity of about 0.7 to 1.3.
 3. The processaccording to claim 1 wherein the tetramethyltetrahydrofuran is contactedwith the alkali metal exchanged alumino-silicate zeolite at atemperature in the range of from about 200* to 350* C at a liquid hourlyspace velocity of about 0.5 to 1.3.
 4. A process for the preparation ofa mixture of 2,5-dimethylhexadiene-2,4 and 2,5-dimethylhexadiene-1,4which comprises contacting tetrahydrofuran in a vapor phase with acatalyst selected from the group consisting of platinum-on-alumina andactivated alumina at an elevated temperature, wherein said temperatureis no greater than 360* C when the platinum-on-alumina catalyst isemployed.
 5. The process according to claim 4 wherein thetetramethyltetrahydrofuran is contacted with the platinum-on-aluminacatalyst at a temperature in the range of from about 350* to 370* C at aliquid hourly space velocity of about 0.7 to 1.3.
 6. The processaccording to claim 4 wherein the tetramethyltetrahydrofuran is contactedwith the activated alumina catalyst at a temperature of from about 200*to 270* C, at a liquid hourly space velocity of about 0.5 to 1.3.
 7. Aprocess foR the preparation of a mixture of 2,5-dimethylhexadiene-1,5and 2,5-dimethylhexadiene-1,4, which comprises contactingtetramethyltetrahydrofuran in a vapor phase with a catalyst comprisingan alkali metal exchanged aluminum silicate - aluminum oxide mixtureoxide at an elevated temperature.
 8. The process according to claim 7wherein the reaction is carried out at a temperature in the range offrom about 475* to 525* C, at a liquid hourly space velocity of about0.8 to 1.2.